The proposed research will extend observations on rhesus monkeys already exposed to delta 9-THC for more than one year at levels comparable to heavy marihuana use in man. During this period, THC daily dosage will be increased and the treatment period extended to permit more conclusive assessment of THC-induced effects related to drug dependence, changes in affect and social behavior, impairment of reproductive function, inhibition of cellular immunological response, and brain histopathology associated with cerebral atrophy. Offspring of THC-treated females will be closely observed for decrements in adaptability and responsiveness during behavioral, neurologic, and neuroendocrine development. The study is designed to utilize to full potential our existing long-term THC treated monkeys in studies relevant to the major controversial issues over potentially harmful effects of marihuana, both 1) in young adults after long-term heavy use, and 2) in infants after exposure to maternal levels of the drug during critical pre- and postnatal periods of neurological development.